1. Field of the Invention
The present invention relates to a lens for use in reproducing data recorded in a medium, such as, for example, an “HD DVD” (High Definition DVD) disk, or in recording data in a medium, and to an optical pickup device equipped with such lens.
2. Description of the Related Art
FIG. 5 is an illustrative drawing showing a figure of a conventional lens, FIG. 6 is an illustrative drawing showing a normal spot, and FIG. 7 is an illustrative drawing showing a spot with coma aberration.
Previously, tilt of an OBL (OBL=Objective Lens) holder (not shown in any of the figures) has been adjusted so that the posture of an objective lens 101 is made parallel to an axis reference of an optical pickup device (not shown) while examining a reflective annular zone A face 130 on an objective lens surface with an auto-collimator (not shown). An auto-collimator here refers to a measuring gauge for measuring a property such as, for example, straightness, perpendicularity, parallelism, or flatness while irradiating light to a target surface, such as a level block or a guide surface.
As a conventional one, for example, there is an objective lens for an optical head device in which an ingenious plan is made for a lens shape in order to simply carry out operation of adjusting a tilt angle when mounting an objective lens for an optical head device to an objective lens-driving mechanism, or determining the aberration of OBL lens.
When laser light is focused onto an optical recording disc using an optical head device equipped with a high quality OBL, the shape of a spot Sa (FIG. 6) focused and formed on an optical recording disc is approximately a regular circle.
In the above-described conventional lens 101 (FIG. 5), however, because the tilt of reflective annular zone A face 130 is not necessarily equivalent to the coma aberration resulting from OBL 101, adjustment of the tilt of OBL 101 using the reflective annular zone A face 130 results in generation of coma aberration for an imaged spot Sb as shown in FIG. 7. In FIG. 5, to facilitate understanding of the OBL 101 in a defective state, a defective state of curved lens faces 110, 120 is shown in an exaggerated form.